In order to manufacture a semiconductor integrated circuit, various heat treatments such as a film forming process for forming, e.g., a silicon film or a silicon oxide film, an oxidation process and the like are performed on a substrate surface. When the heat treatments are carried out, there is often used a so-called batch type heat treatment apparatus capable of simultaneously processing a plurality of semiconductor wafers (hereinafter, simply referred to as a “wafers”).
The batch type heat treatment apparatus employs a method for heating a reaction tube in which a plurality of wafers is accommodated by using an electric furnace (hot wall). However, the method using an electric furnace is disadvantageous in that a long period of time is required to increase or decrease a wafer temperature due to large heat capacity of the entire furnace to thereby decrease productivity remarkably.
In addition, there is known a heat treatment apparatus for heating a wafer through high-frequency induction heating (see, e.g., Japanese Patent Applications Publication Nos. S56-006428 and S61-091920). This heat treatment apparatus generally includes an induction coil externally wound around a reaction tube and supplies a high frequency current to the induction coil, to thereby inductively heat a conductive susceptor provided in the reaction tube. Accordingly, a wafer mounted on the susceptor is indirectly heated by the heat conduction. Since, with such configuration, it becomes unnecessary to directly heat the reaction tube, this can reduce the heat capacity of the susceptor and, thus, the wafer temperature can be increased or decreased at a high speed compared to the case of using an electric furnace. Further, it is possible to control a wall temperature of the reaction tube separately from the wafer temperature as in a so-called cold wall type heat treatment apparatus.
However, if the high frequency induction heating is performed in the cold wall type heat treatment apparatus having a plurality of susceptors of small heat capacity, in-plane temperature uniformity of the susceptors and/or temperature uniformity between the susceptors are deteriorated due to a difference between temperatures of the susceptors and an ambient temperature (e.g., temperatures of inner walls of the reaction tube and the like). Furthermore, temperature uniformity between a plurality of wafers and in-plane temperature uniformity of each wafer may be deteriorated.
As for a method for improving temperature uniformity between wafers, there is disclosed in, e.g., Japanese Patent Application Publication No. 2003-017426 for controlling temperature uniformity between wafers by individually controlling powers supplied to a plurality of induction coils arranged in a lengthwise direction of the reaction tube. Moreover, in, e.g., Japanese Patent Application Publication No. 2003-068658, wafers are arranged between inductively heated dummy heating plates to improve the temperature uniformity.
However, no prior art has disclosed a method for controlling temperature uniformity of each wafer, and there has not yet been known a method for controlling in-plane temperature uniformity of wafers which can be applied to a batch type heat treatment apparatus for processing a plurality of wafers simultaneously.